1. Field of the Invention
The present invention relates to an elevator comprising an elevator shaft with guide rails on which the elevator car and its counterweight move, the ropes on which the car and counterweight are suspended, and a traction sheave, whose motion is transmitted to the car and counterweight by the ropes.
2. Description of Related Art
To increase the transportation capacity of an elevator in relation to the total volume of the elevator structures, an expedient commonly used is to increase the transportation capacity relative to time e.g. by increasing the travelling speed of the elevator or by appropriate arrangements in the organization of elevator traffic, e.g. by shortening the stays at floor levels between stopping and departure.
Another way to increase the transportation capacity in relation to the volume of the elevator structures is to reduce the total volume of the elevator. To achieve a reduction in the total volume, it is hardly possible to reduce the size of the machine room to any significant extent. Neither can the height of the elevator shaft be reduced without reducing the travel height or speed of the elevator.
Thus, the only recourse available is to increase the ratio of the area of the horizontal section of the elevator car to the sectional area of the shaft. To achieve this, the layout of the elevator components on the transverse plane in the shaft is generally designed with a view to increasing the car area. In the transverse layout, within the limitations imposed by the functional properties of the components, a nearly optimum state has already been achieved.
Another problem with current elevator suspension arrangements where the counterweight speed and travel are equal to those of the car is that, in cases of failure where the car and counterweight "break loose", the sudden stop resulting from the action of the safety gear leads to a so-called bound of the counterweight, for which reason the elevator shaft must provide enough headroom for this counterweight bound at the upper end to avoid damage to the machinery or the shaft ceiling.
Another factor which imposes certain restrictions on the design of the elevator shaft is the height of the counterweight, because the counterweight travel is essentially equal to the car travel.